The present invention relates to a magnetic resonance signal receiving method and apparatus and a magnetic resonance imaging apparatus, and more particularly to a magnetic resonance signal receiving method and apparatus for receiving a spin echo from spins that lie in two slices intersecting each other and are excited by 90xc2x0 and 180xc2x0, respectively, while translating the intersection in an imaged space, and a magnetic resonance imaging apparatus employing such a magnetic resonance signal receiving apparatus.
As exemplarily shown in FIG. 1, magnetic resonance imaging by line scanning involves exciting spins lying in two slices 90a and 180a intersecting each other by 90xc2x0 and 180xc2x0, respectively, receiving a spin echo generated at the intersection aa of the slices, and performing a one-dimensional inverse Fourier transformation on the received spin echo to reconstruct a line image relating to the intersection aa.
By changing the combination of slices to be excited by 90xc2x0 and 180xc2x0, the intersection is sequentially translated as indicated by bb, cc, dd . . . , to sequentially obtain a plurality of line images, and an image for one screen is produced from a set of the line images.
In line scanning, the effect of body motion of the imaged object is limited to the line image acquired when the body motion happens to occur, and does not affect the whole image. Taking advantage of this characteristic, line scanning is used for acquiring diffusion images, which especially tend to be affected by body motion.
In such line scanning, a slice excited by 90xc2x0, e.g., 90a, will subsequently intersect a 180xc2x0 excited slice 180b for imaging a next line bb, a 180xc2x0 excited slice 180c for imaging a following line cc, and a 180xc2x0 excited slice 180d for imaging a next following line dd, and so forth. Therefore, if spins in the 90xc2x0 excited slice 90a are not fully relaxed, spin echoes are generated at intesections with these 180xc2x0 slices, i.e., ab, ac and ad. This is also true for other 90xc2x0 excited slices 90b, 90c and 90d which generate spin echoes at intersections bc, cd, and bd.
Because such spin echoes have the same timing as spin echoes of proper lines to be acquired thereafter, the reconstructed image comes to contain artifacts, resulting in lower quality.
It is thereefore an object of the invention to provide a magnetic resonance signal receiving method and apparatus for preforming imaging with good quality, and a magnetic resonance imaging apparatus employing such a magnetic resonance signal receiving apparatus.
In accordance with a first aspect of the invention, there is provided a magnetic resonance signal receiving method for receiving a spin echo from spins that lie in two slices intersecting each other and are excited by 90xc2x0 and 180xc2x0, respectively, while translating the intersection in a imaged space, comprising applying a grdient magnetic field for dephasing spins whose strength is varied after each spin echo is received.
In accordance a second aspect of the invention, there is provided a magnetic resonance signal receiving apparartus for receiving a spin echo from spins that lie in two slices intersecting each other and are excited by 90xc2x0 and 180xc2x0, respectively, while translating the intersection in an imaged space, comprising gradient magnetic field appling means for applying a gradient magnetic field for dephasing spins whose strength is varied after each spin echo is received.
In accordance with a third aspect of the invention, there is provided a magnetic resonance imaging apparatus for periodically receiving a spin echo from spins that lie in two slices intersecting each other and are excited by 90xc2x0 and 180xc2x0, respectively, while translating the intersection in an imaged space, and producing an image based on the received spin echo, comprising gradient magnetic field applying means for applying a gradient magnetic field for dephasing spins whose strength is varied after each spin echo is received.
(EFFECT)
According to the present invention, by applying a gradient magnetic field for dephasing spins whose strength is varied after each spin echo is received, generation of an unwanted spin echo is prevented.
Thus, the present invention can provide a magnetic resonance signal receiving method and apparatus for performing imaging with good quality, and a magnetic resonance imaging apparatus employing such a magnetic resonance signal receiving apparatus.